Dockboard raising mechanism

ABSTRACT

A dockboard raising mechanism for a dockboard installation in which the dockboard is hingedly attached at its rear end to the base part, the mechanism including a lever and a link pivotally connected together at their inner ends, and having their outer ends attached to pivots respectively on the dockboard and base parts, the mechanism being powered by a hydraulic cylinder acting between a pivot on the base part and an intermediate pivot point on the lever. This mechanism is compact both vertically and longitudinally, maintains a fairly constant direction of force on the dockboard, and can be arranged to maintain a rearwards force on the dockboard to prevent dislocation of a floating hinge.

United States Patent Loblick 1 1 Oct. 3, 1972 DOCKBOARD RAISING MECHANISM [72] Inventor: Dermont F. Loblick, Gibbons, Al-

berta, Canada 22 Filed: June 26,1970

211 Appl.No.: 50,255

[30] Foreign Application Priority Data July 4, 1969 Great Britain ..33,904/69 [52]' US. Cl. ..14/71 [51] Int. Cl ..B65g 11/00 [58] Field of Search 14/71 [56] References Cited UNITED STATES PATENTS 2,689,965 9/1954 Fenton 14/71 3,305,885 2/1967 Vaillant 14/1 FOREIGN PATENTS OR APPLICATIONS 723,723 2/ 1955 Great Britain ..l4/71 Primary Examiner-Jacob L. Nackenoff Att0rney--Cushman, Darby & Cushman [5 7 ABSTRACT A dockboard raising mechanism for a dockboard installation in which the dockboard is hingedly attached at its rear end to the base part, the mechanism including a lever and a link pivotally connected together at their inner ends, and having their outer ends attached to pivots respectively on the dockboard and base parts, the mechanism being powered by a hydraulic cylinder acting between a pivot on the base part and an intermediate pivot point on the lever. This mechanism is compact both vertically and longitudinally, maintains a fairly constant direction of force on the dockboard, and can be arranged to maintain a rearwards force on the dockboard to prevent dislocation of a floating hinge.

10 Claims, 7 Drawing Figures PATENTEDUET 3 m2 SHEET 1 OF 6 FIGI Mummers m2 I v 3.694.840

SHEET t UP 6 j FIGS Mi/S DOCKBOARD RAISING MECHANISM The present invention relates to dockboard installations, i.e.,'i nstallations whichare used to provide a sloping ramp or dock plate connecting the floor of a warehouse bay or like facility to the platform of a vehicle being loaded or unloaded.

Warehouses and like places generally have loading and unloading bays which are raised from ground level so as to be of similar height to the load carrying platforms of the vehicles which are serving the bay. 'In order for goods to be moved readily from the vehicle platformsand onto the loading bay and vice versa, it is necessary to provide a dockboardwhich spans the'gap between the vehicle and the loading bay, and which also provides a ramp from the loading bay to the vehicle where these are not quite level. Various types of dockboard installations have been developed which include a base part to which the dockboard is hinged at its rear end, and which incorporate a mechanism for raising the dockboard and lowering this onto the platform of a vehicle; such mechanisms may be either mechanical, for example hand or spring operated, or hydraulically operated. The dockboards generally include an extendible lip at their outer edge which rests on the vehicle platform, andknown dockboards have lips which are hinged to the outer edge of the dockboard and which extend when the dockboard is raised, but which fold away flush with the edge of the loading bay when the board is lowered ,and not in use.

Present known dockboard raising mechanisms are of many types which suffer from various drawbacks. Many such mechanisms are spring operated; in this case the maintainence of spring tensions over a long period can give problems, and in addition there are dangers inherent in having a large amount of energy stored in springs. Hydraulic systems are also very common, but none of these known hydraulic systems have all the desiderata of a dockboardraising mechanism. These desiderata are:

l. The combination of small overall height of mechanism (in the collapsed state) with relatively large range of vertical movement. The overall height determines the pit depth required.fortheinstallation, which is an important item of expense, and the range of vertical movement determines the suitability of the installation for different vehicles.

2. The mechanism should apply a reasonably constant liftforce to thedockboard throughout its range of movement, otherwise the power being supplied to the hydraulic cylinder will be wasted over a part of its stroke.

3. To avoid undue strain on the dockboard hinge, the force applied by the lifting mechanism should preferably act roughly perpendicularly to the dockboard. However, where a floating hinge is used (as will be described) this may require that a rearwards component of force be maintained on the dockboard.

4. According to the type of hinge, it may also be required to avoid a large overhang of the dockboard in front of the raising mechanism, such as would cause an upwards force to be applied by the dockboard to the hinge.

Other desirable features of such mechanisms will be obvious to an engineer, for example that they should be compact, use a minimum number of parts and pivots,

and should employ links in tension rather than in compression.

' Known hydraulic systems do not possess many or all of these features. For example, some systems use a piston and cylinder combination connected directly between a base member and the dockboard. In at least .one known system, the cylinder is substantially vertical,

in which case either a short cylinder or a deep pit must be used, so that such systems do not generally meet desiderata (l) and (4) above. Alternatively, if the cylinder is inclined at a substantial angle to the vertical, to give a small overall height of mechanism, the force cannot be applied-anywhere near perpendicularly to the dockboard, and desiderata (2) and (3) are not met.

Further hydraulic systems are known in which the hydraulic piston and cylinder combination, instead of acting directly on the dockboard, acts on one lever of a bell crank or like member having its other lever connected to the dockboard by a compression link. Such arrangements are shown for example in US. Pat. No.

2,689,965 (Fenton) and U.S. Pat. No. 3,235,895

(Wallace). Such arrangements allow an increased initial lifting force to be applied by a hydraulic cylinder mounted in the nearhorizontal position. However, in these systems the direction in which lifting force is applied to the dockboard, which coincides with the direction of the compression link, varies as the dockboard is raised. In the specific designs shown in these prior patents the extent of this variation is not unduly large since the extent of movement of the dockboard is small in relation to pit depth. However this variation would increase if these designs were to be adapted to give a large amount of dockboard lift relative to the depth of pit, as is desirable. Accordingly, these known hydraulic/mechanical arrangements do not adequately fulfill all the desiderata l (2) and (3) as set outabove.

The main object of the present invention is to provide ahydraulic/mechanical system which overcomes the drawbacks of the known systems described above, and which, with suitable arrangement and proportioningof its parts, can substantially meet all the desiderata set out above.

A dockboard installation according to the present invention is similar to the Fenton and Wallace designs referred to above in having a base part and a dockboard part hingedly connected at its rear end to the base part, these parts being also connected together by a mechanism including a lever and a link pivotally connected at their inner ends and having their outer ends attached to pivots respectively on the dockboard and base parts. The lever is also connected to a piston and power cylinder combination, but unlike in the Fenton and Wallace patents, the piston and cylinder combination has one end connected to a pivot on the lever intermediate its ends and has its other end pivotally connected to the same part to which the outer end of the link is attached. Thus, the lever is acted upon by the cylinder force at the intermediate pivot and the outer end of the lever serves to magnify the movement provided by the extension of the power cylinder.

Conveniently, the link is attached at its outer end to the base part and the lever is attached at its outer end to the dockboard, the power cylinder being pivotally mounted on the base part.

This basic mechanism is of course susceptible to considerable variation depending on specific requirements. However, preferred arrangements of this basic mechanism have the following additional characteristics:

a. The pivotal mounting for the power cylinder on the base part is preferably close to the pivot connecting the link to the base part. This has a number of effects,

for example it ensures that the direction of lifting forceapplied to the dockboard does not vary unduly as the dockboard is raised, and also ensures that the link can remain in tension throughout the range of movement of the dockboard. Furthermore, this feature will ensure that the mechanism is compact in the longitudinal direction of the cylinder.

b. The mechanism is preferably designed so that the lifting force applied to the dockboard maintains a rearward component of force at all times on the dockboard, thus allowing a simple type of floating hinge (to be described) to be used at the rear end of the dockboard. The advantage ofthis floating hinge is that it allows the dockboard to adjust itself to vehicles which are not horizontal, by allowing the dockboard to rock about a fore-and-aft axis. A suitable and very simple floating hinge takes the form of a horizontal forwardly projecting rib attached to the rear of the base of the installation, and a flange projecting from the rear end of the dockboard and resting on the top of the rib in a manner which allows for the desired rocking movement. This hinge construction requires means for holding the flange on the rib, to prevent dislocation. The mechanism of this invention can readily perform this function; for example, if the pivots connecting the cylinder and the link to the base are at all times forward of the lever/dockboard pivot, then the mechanism maintains a rearwards force on the dockboard at all times when the mechanism is supporting the dockboard. In the at rest condition, catch means are provided for holding the dockboard in place.

c. Preferably, the link and lever are arranged to fold rearwardly of a line joining their end pivots. With this arrangement, the end pivot of the lever can be situated fairly near the outer end of the dockboard, avoiding a large overhang of the dockboard beyond this lifting point.

In -a preferred embodiment of the invention, the pivot connecting the link to the base coincides with the pivotal mounting for the cylinder on the base, so that a single pivot pin can be used to connect both the link and the cylinder to the base. In this case, the mechanism requires only four pivots compared to five of the prior Fenton and Wallace patents referred to above. This arrangement is very compact in the longitudinal direction of the cylinder, since the cylinder is at all times wholly within the area bounded by the four pivots on the lever and link. Furthermore, with this arrangement the force applied must always act on a line through the outer end pivots of the link and lever, so that it is a simple matter to design this mechanism so that it applies a lifting force roughly perpendicularly to the dockboard, but with a rearwards component where this is required to prevent dislocation of a floating type hinge.

The position of the intermediate pivot point on the lever can be chosen so that a fairly large lifting force is pivots of the lever, so that the lever thus takes the form of a bell crank.

The dockboard installation in accordance with this invention also incorporates a novel mechanism for raising an extendible lip; this mechanism is the subject of copending U.S. Pat. application Ser. No. 50,098. Also, the installation includes a novel hydraulic circuit and control means, which is the subject of copending U.S. Pat. application Ser. No. 50,256, filed June 26, I970.

The present invention will be particularly described by way of example with reference to the accompanying drawings showing preferred embodiments thereof, in which:

FIGS. 1 and 2 are schematic drawings of a dockboard raising mechanism in different positions,

FIG. 3 is a perspective view of a dockboard installation,

FIGS. 4 and 5 are side sectional elevations of the same dockboard in various operational positions,

FIG. 6 is an enlarged cross-sectional view of hinge means used in the embodiment of FIG. 1 to 5, and

FIG. 7 is a side sectional elevation of a similar dockboard installation which is adapted to occupy less vertical height than that of FIGS. 1 to 5.

Referring to FIGS. 1 to 5, the dockboard is shown mounted in a recess or pit in the side of a loading bay 10, so that the top of the dockboard is level with the loading bay in its horizontal position (FIG. 5). The installation includes a base frame 12 which fits within the pit and which includes longitudinal, transverse and upright members and which forms a support structure for the dockboard and its raising mechanism. The mechanical parts of the installation, i.e., the base frame, the dockboard, and the raising mechanism, form a self-contained unit.

At the rear end of the base frame a special floating hinge is provided (FIG. 6), including a transverse forwardly projecting rib 15 attached to the upper rear cross-member 16 of the frame, which rib is engaged by a horizontal flange l7 projecting rearwardly from the rear end of the dockboard. The flange 17, which is in this case the top flange of a channel member, rests on the top of the rib, and abuts against a shallow step 18 at the rear edge of the rib formed by an upwards projection of the cross-member 16. As is clear from FIG. 6, the rib 15 has a downwardly sloping and slightly curved uppersurface, which allows the dockboard to move between its extreme positions while maintaining an almost gap-free transition between the upper rear surface of the base structure and the dockboard. This hinge is also floating in that it allows a slight rocking movement of the dockboard to occur about its fore-and-aft axis, whereby the forward end of the dockboard can rest flush with a vehicle platform even if the platform is not level. Clearly, a rearwards force must be maintained on the dockboard to prevent dislocation of the hinge.

As shown in FIGS 1 and 2, the basic hydraulic/mechanical system for raising the dockboard comprises a lever 20 and a link 21, connected together at their inner ends by a pivot 22, the outer end of the lever being connected to the dockboard 11 by means of a pivot 24, and the outer end of the link 21 being connected to the base by a pivot 25. Pivot 25 is situated so as to be at all times forward of the pivot 24. A hydraulic cylinder 26 is pivotally attached to the base by means of the same pivot 25 which holds the outer end of the link, and the piston rod 27 of this cylinder is connected to a pivot point 29 on the lever intermediate the end 48 moves above the line joining-the pivots 43 and 50. Accordingly, once the lip has been raised by pulling the rod 55 so that pivot 48 passes over center, the lip remains raised without any further tension being maintained in the rod, until either the rod 55 is forced forwards or untilthe lip is tripped in a manner to be pivots 22 and 24. The operation of the system is apparent from FIGS. 1 and 2; it will be seen that as the piston rod 27 extends the lever 20 is caused to rotate primarily about pivot 22, where it is held by the link 21,

so that the outer end of the lever magnifies the movement of the piston rod in raising the dockboard. In order for the piston rod to exert adequate turning moment on the lever in the fully collapsed condition (FIG. 2), the intermediate pivot point 29 is spaced above a line joining the end pivot points 22 and 24, so that the lever takes the form of an obtuse-angled bell crank.

As will be seen from FIG. 3, 4 and 5, particularly FIG. 3, in practice the lever 20 consists of two parallel plates, linked by rods forming the pivots 22, 24 and 29. The outer end of the piston rod 27 acts at the center of pivot rod 29. The center of pivot rod 24 is attached to a sleeve member 31 extending fore-and-aft of the dockboard and rotatable on a pin held by a bracket 32, and this arrangement allows rocking motion of the dockboard about a fore-and-aft axis (as permitted by the floating hinge) to occur without bending the raising mechanism. The link 21 is also formed by two parallel link members, spaced on opposite sides of the cylinder 26, and connected to longitudinal base members 34 by pivot rod 25 which also provides a pivotal mounting for the base of cylinder 26.

The dockboard of the present invention also has a novel lip operating mechanism (the subject of copending US. patent application Ser. No. 50,098) by means of which a lip hinged to the outer edge of the dockboard is raised while the dockboard is raised, and remains in a raised condition until tripped by contact with a vehicle platform, or until the dockboard is finally lowered.

Pivoting of the lip 40 about its hinge 41 between the raised position (inwhich the lip forms an extension of the dockboard) to the lowered position (at right angles to the dockboard) is effected by means of two parallel links 42 (shown best in FIG. 3) having their outer ends pivoted at 43 to an arm 44 extending downwardly from the lip, the links passing rearwardly through an opening in the front flange 46 of the dockboard.

The rear ends of links 42 are pivotally connected at 48 to one end of a crank member 49 which is centrally pivoted at 50 to a bracket 51 fixed to the lower side of the dockboard. The other end of crank member 49 is pivotally connected at 53 to a yoke member 54 attached to the forward end of a rod 55. A stop 56 is provided to limit rotation of crank member 49. The crank member 49 is in the form of a bell crank having an obtuse angle defined by its two arms, i.e., the central pivot 50 is displaced below a line joining the end pivots 48 and 53. The arrangement is such that on pulling of the rod 55 rearwardly the member is rotated anti-clockwise (as viewed in FIG. 4) and the links 42 are urged forwards so raising the lip, and in the final stage of movement the links 42 pass over center, i.e., the pivot point described.

The inner end of rod 55 carries a slidable crossmember 57, the travel of which is limitedby a nut 58 secured to the screwed outer end of the rod. The crossmember 57 carries a pivot pin at each end which engage in opposite arms of a bracket 60, this bracket forming one arm of a bell crank member 61 pivoted at 62 to a longitudinal member 63 fixed to the under side of the dockboard. The other arm of crank 61 is provided with a slot in which a pin 64 is slidable, this pin 64 connecting two side plates of a link 65, one of which side plates is extended and pivoted at 66 to the intermediate pivot rod of the lever 20. The link member 65 thus forms the connecting link between the dockboard raising mechanism and the lip raising mechanism.

The operation of the lip raising mechanism is as follows:

In the initial horizontal position of the dockboard (shown in full lines in FIG. 5) the pin 64 of link 65 is at the outer end of the slot in crank 61, the crank 61 is ina position in which the slotted end is close to the dockboard, the rod 55 is thus in a forward position, and the lip 46 is hanging vertically. As the dockboard is raised by extension of piston rod 27 and the mechanism described previously, the intermediate pivot point 29 (which coincides with pivot 66) of the lever 20 moves away from the underneath of the dockboard, pulling with it the link 65 and causing pin 64 to move to the inner end of its slot. Since the pin 64 is free to move in this slot, and since the link 65 is free to swivel about pivot point 66, no turning moment is experienced by crank 61 in this initial raising movement, which continues until the dockboard has been raised to an intermediate position about half-way up to its final position. Due to the lost motion provided for in the linkage by the slot in crank 61, the lip 46 remains hanging during this initial movement, and does not catch against a vehicle backed up against the dockboard.

When the pin 64 reaches the inner end of the slot in crank 61, further raising of the dockboard causes the link 65 to come into tension, and this rotates the crank 61 anti-clockwise (referring to the side elevational views). This rotation moves the rod 55 rearwardly, and causes the crank member 49 to swivel and raise the lip 40 to its extended position, in the manner already explained.

From this upper position with the lip raised, the dockboard is slowly lowered until the lip 40 comes to rest on the platform of a vehicle. The engagement of the lip on the platform then supports the dockboard while a vehicle is being loaded or unloaded.

These movements may be made automatic by connecting cylinder 26 to a hydraulic circuit by means of which the cylinder is extended by operation of a hydraulic pump, the cylinder being automatically lowered slowly when pump operation ceases.

During this initial lowering movement, crank 61 rotates slightly clockwise (as viewed in FIG. 4), but member 57 slides on the rod 55 so that although tension in the road is removed, the rod is not forced forwardly and the lip remains raised by virtue of the overcenter-position of the pivot 48. When the lip engages the vehicle platform, it is raised slightly relative to the dockboard so that links 42 are put in tension and, since road 55 is not under tension, the crank 49 rotates slightly clockwise, until due to weight of links 42, the pivot point 48 eventually assumes a'below center position with respect to pivot points 43 and 50. Thus the mechanism which holds the lip raised is tripped once the lip has come into contact with a vehicle, and when the vehicle drives away the lip automatically falls, with rod 55 sliding within member 57.

As is clear from FIG. 5, the dock plate not only provides an upwards ramp for vehicles having a platform which is higher than the loading bay, but also provides a downwards ramp for use when the vehicle is slightly lower than the loading bay. In order for the docking plate to reach the lowest position, which is shown ghosted in FIG. 5, the hydraulic controls are operated so that the dockboard rises in the manner previously described until the lip 40 has been fully extended, and then falls slowly under gravity with fluid being returned from the cylinder 26 into a fluid reservoir, until the lip finally contacts the vehicle, for example when the lip is near to the lowest position shown in FIG. 5. The engagement of the lip on the vehicle platform trips the lip raising mechanism as described, and when the vehicle has moved away the lip drops and the dockboard continues to descend until a timed limit switch 70 is actuated by the end of lever 20. This limit switch causes an electrical contact to be made to start the hydraulic pump motor to pressurize cylinder 26 causing the dockboard to rise just above the horizontal position, after which the limit switch 70 de-energizes the pump motor and the hydraulic circuit again allows the dockboard to descend-under gravity. The outer edge of the lip 40 is caught in a support bracket 71 forming the outer edge of the frame 12, and all parts of the mechanism are at rest in the position shown in full lines in FIG. 5. In this position, the engagement of the lip 40 in the bracket 71 gives firm support to the dockboard.

The limit switch 70 also comes into action in the event of the dockboard being raised and lowered without contacting a vehicle platform. In this case, the dockboard again lowers itself to the lowest position of FIG. at which the lever 20 actuates the time limit switch 70 and the dockboard is again raised to a position in which the lip can fall down and be caught behind the outer edge of the frame 2. In this case, the lip operating mechanism is automatically collapsed by an adjustable stop 73 positioned on the frame to strike the rear portion of crank 49 when the dockboard is in its lowest position, so rotating the crank 49 and tripping the lip.

FIG. 7 shows a surface mounted dockboard, i.e., a dockboard installation which is intended to be mounted on a loading bay without the provision of any pit. In this case, the inner end of the dockboard installation includes a 6-inch channel 80 and a ramp is provided (not shown) to provide suitably sloped access to this channel. All the mechanical elements of this modified dockboard installation are similar to that previously described, except that it is arranged for the mechanism to be folded down to its most compact condition when the dockboard is horizontal, rather than when the dockboard is sloping downwardly. It will be seen that this arrangement occupies very little vertical height, in practice about 6 inches, as compared to about 17 to 20 inches height common with known mechanisms, at least those giving a reasonably high lift. It will also be noted that with this arrangement the lip 40 overhangs the edge of the loading bay.

Referring again to the schematic arrangement of FIGS. 1 and 2, it will be clear that the mechanism comprised by lever 20, link 21, the piston and cylinder combination 26, 27, and their connecting pivots, can be regarded as a self-contained unit, which applies a force to the dockboard which always acts on the line through pivots 24 and 25. Accordingly, the direction of force applied to the dockboard varies comparatively little during the whole movement from the fully raised condition of FIG. 1 to the fully collapsed condition of FIG. 2; in fact the alteration in the angle of applied force is about 30, which is relatively small considering the range of movement involved. This means that the force can readily be maintained at a desired angle so as to give a reasonably constant rearward force component on the hinge; the arrangement illustrated is almost ideal in this case since the force rearward force component is at a maximum when the dockboard is the collapsed condition where the weight of the dockboard itself would otherwise tend to dislocate the hinge. In short, the mechanism of this invention meets all the desiderata set out above, and also has further advantages over the known bell crank arrangements, namely:

1. Only four pivots are required instead of five;

2. The link 21 is in constant tension, and so is not required to be rigid;

3. The mechanism is very compact in the fore-andaft direction, as well as vertically.

It will be clear that, even if the link and the cylinder are connected to the base by separate, spaced apart, pivots, many advantages remain in accordance with the invention. For example, where these pivots are suff1- ciently close, the link will always remain in tension throughout the whole range of dockboard movement, and so need not be designed to resist compressive forces. Likewise, with these pivots relatively close, the direction in which force is applied to the dockboard remains relatively constant, and it can easily be arranged to maintain a rearwards component of force on the dock board to prevent dislocation of a floating hinge. Also, the mechanism remains relatively compact provided that at least a major portion of the piston and cylinder combination lies within an area defined by the four pivots of the lever and the link.

Also, it will be understood that the mechanism can also be mounted in a variety of different ways. For example, the link, lever, and piston and cylinder combination can be reversed end for end from the position shown in the drawings, so that the lever acts on the base and the link and cylinder are attached to the dockboard. Also the mechanism can be rotated about an axis through its ends, for example through so that the link and lever fold forwardly rather than rearwardly; this however would necessitate that the mechanism be also set back somewhat rearwardly giv ing increased overhang of the dockboard over its point of lift.

I claim:

l. A dockboard installation including a base part and a dockboard part hinged at its rear end to. said base part, and a dockboard raising mechanism connecting said parts and comprising a lever and a link pivotally connected together at their inner ends, the outer end of the lever being pivoted to said dockboard part and the outer end of the link being pivoted to said base part, and further comprising a power cylinder pivotally mounted on said base part and having its piston rod attached to an intermediate pivot on said lever.

2. A dockboard installation according to claim 1, wherein the dockboard part is hinged to the base part by hinge means comprising an upwardly facing surface fixed to said base part and a co-acting downwardly facing surface fixed to said dockboard part, and means limiting rearwards movement of the dockboard part relative to the base part, and wherein the pivots connecting the link and power cylinder to the base are positioned so as to be at all times in front of the pivot connecting the lever to the dockboard part, whereby the raising mechanism maintains a rearwards force on the dockboard at all times when the mechanism is supporting the dockboard.

3'. A dockboard installation according to claim 2, wherein the said hinge means includes a forwardly projecting horizontal rib attached to the base part and a flange projecting from the rear end of the dockboard part and resting on the top of said rib, the edge of said flange abutting against a shallow step at the rear of said rib.

I 4. A dockboard installation according to claim 1 wherein at least a major portion of the piston and cylinder combination lies within an area defined by the four pivots of the lever and link, i.e., by the pivot connecting the lever and link, the pivots at the outer ends of the lever and the link, and by the intermediate pivot of the lever.

. 5. A dockboard installation according to claim 1, wherein the pivot attaching the outer end of the link to the base coincides with the pivotal mounting of the power cylinder on the base.

6. A dockboard installation according to claim 5, wherein the said intermediate pivot on the lever is spaced above a line joining the end pivots of the lever, whereby the lever takes the form of a bell crank.

7. A dockboard installation according to claim 1, wherein the said lever is constituted by two parallel side plates spaced apart so as to locate one at each side of the cylinder when the dockboard is collapsed.

8. A dockboard installation according to claim 1 wherein the link and lever are arranged to fold rearwardly of a line joining their outer end pivots.

9. A dockboard installation including a base part and a dockboard part hinged at its rear end to said base part, and a dockboard raising mechanism connecting said. parts and comprising a lever and a link pivotally connected together at their inner ends, the outer end of the lever being pivoted to said dockboard part and the outer end of the link being attached to a link pivot on the base part, and further comprising a piston and power cylinder combination having one end attached to an intennediate pivot on the lever and having the other end attached to a cylinder pivot on the said base part said cylinder pivot being on the same side of the lever as the link pivot and being also positioned to raise the dockboard when the pisto and cylinder combinatron 15 extended, whereby the ink lS maintained in tension at all times.

10. A dockboard installation comprising:

a base having a raised rear portion and a depressed forward portion;

means defining a first hinge portion on the raised rear portion of the base;

a dockboard having a rear edge and a forward edge;

means defining a second hinge portion on the i dockboard adjacent the rear edge thereof;

the second hinge portion resting upon and being pivotal about the first hinge portion, with the dockboard extending forwardly over the depressed forward portion of the base;

a normally inextensible lever;

first pivot means pivotally securing one end of said lever to the dockboard, forwardly of said hinge portions;

a normally inextensible link;

second pivot means pivotally securing one end of said link to the base within the depressed forward portion thereof, forwardly of said hinge portions;

third pivot means pivotally securing the opposite end of the lever to the opposite end of the link, said third pivot means being disposed closer to said hinge means than are said first and said second pivot means;

an extensible/retractable strut;

said second pivot means pivotally mounting one end of said extensible/retractable strut;

fourth pivot means pivotally securing the opposite end of the extensible/retractable strut to the lever, said fourth pivot means being disposed rearwardly of a plane containing the first pivot means and the second pivot means, whereby said lever functions as a bell crank, and whereby the raising mechanism constituted by all said pivot means, said lever, said link and said extensible/retractable strut maintains a rearward force on the dockboard while the raising mechanism supports the dockboard forwardly of said hinge members. 

1. A dockboard installation including a base part and a dockboard part hinged at its rear end to said base part, and a dockboard raising mechanism connecting said parts and comprising a lever and a link pivotally connected together at their inner ends, the outer end of the lever being pivoted to said dockboard part and the outer end of the link being pivoted to said base part, and further comprising a power cylinder pivotally mounted on said base part and having its piston rod attached to an intermediate pivot on said lever.
 2. A dockboard installation according to claim 1, wherein the dockboard part is hinged to the base part by hinge means comprising an upwardly facing surface fixed to said base part and a co-acting downwardly facing surface fixed to said dockboard part, and means limiting rearwards movement of the dockboard part relative to the base part, and wherein the pivots connecting the link and power cylinder to the base are positioned so as to be at all times in front of the pivot connecting the lever to the dockboard part, whereby the raising mechanism maintains a rearwards force on the dockboard at all times when the mechanism is supporting the dockboard.
 3. A dockboard installation according to claim 2, wherein the said hinge means includes a forwardly projecting horizontal rib attached to the base part and a flange projecting from the rear end of the dockboard part and resting on the top of said rib, the edge of said flange abutting against a shallow step at the rear of said rib.
 4. A dockboard installation according to claim 1 wherein at least a major portion of the piston and cylinder combination lies within an area defined by the four pivots of the lever and link, i.e., by the pivot connecting the lever and link, the pivots at the outer ends of the lever and the link, and by the intermediate pivot of the lever.
 5. A dockboard installation according to claim 1, wherein the pivot attaching the outer end of the link to the base coincides with the pivotal mounting of the power cylinder on the base.
 6. A dockboard installation according to claim 5, wherein the said intermediate pivot on the lever is spaced above a line joining the end pivots of the lever, whereby the lever takes the form of a bell crank.
 7. A dockboard installation according to claim 1, wherein the said lever is constituted by two parallel side plates spaced apart so as to locate one at each side of the cylinder when the dockboard is collapsed.
 8. A dockboard installation according to claim 1 wherein the link and lever are arranged to fold rearwardly of a line joining their outer end pivots.
 9. A dockboard installation including a base part and a dockboard part hinged at its rear end to said base part, and a dockboard raising mechanism connecting said parts and comprising a lever and a link pivotally connected together at their inner ends, the outer end of the lever being pivoted to said dockboard part and the outer end of the link being attached to a link pivot on the base part, and further comprising a piston and power cylinder combination having one end attached to an intermediate pivot on the lever and having the other end attached to a cylinder pivot on the said base part said cylinder pivot being on the same side of the lever as the link pivot and being also positioned to raise the dockboard when the piston and cylinder combination is extended, whereby the link is maintained in tension at all times.
 10. A dockboard installation comprising: a base having a raised rear portion and a depressed forward portion; means defining a first hinge portion on the raised rear portion of the base; a dockboard having a rear edge and a forward edge; means defining a second hinge portion on the dockboard adjacent the rear edge thereof; the second hinge portion resting upon and being pivotal about the first hinge Portion, with the dockboard extending forwardly over the depressed forward portion of the base; a normally inextensible lever; first pivot means pivotally securing one end of said lever to the dockboard, forwardly of said hinge portions; a normally inextensible link; second pivot means pivotally securing one end of said link to the base within the depressed forward portion thereof, forwardly of said hinge portions; third pivot means pivotally securing the opposite end of the lever to the opposite end of the link, said third pivot means being disposed closer to said hinge means than are said first and said second pivot means; an extensible/retractable strut; said second pivot means pivotally mounting one end of said extensible/retractable strut; fourth pivot means pivotally securing the opposite end of the extensible/retractable strut to the lever, said fourth pivot means being disposed rearwardly of a plane containing the first pivot means and the second pivot means, whereby said lever functions as a bell crank, and whereby the raising mechanism constituted by all said pivot means, said lever, said link and said extensible/retractable strut maintains a rearward force on the dockboard while the raising mechanism supports the dockboard forwardly of said hinge members. 